Hard plant seeds in well-servicing compositions and methods



CONIPOSIHONSAND-NIETHGDS since' nearly alldrillingfluids-andcement Slurriesjcont fi ,Alice, Tex., assignors to. Pan AmericanPetroleum Corpo -alien, a corporation of Delawarefj t g No Drawing. Filed July'15, ;1955 Sel N6. 522,365

29 Claims. cures-.21

of plant seeds, ground to granular form, in wellyserrvicing slurries used in wells for various purposes such as drilling, Work-over, cementing, and the like. t

This application is a continuation-in-part of our appli: cation Serial No. 269,529, filed February 1, 1952, no,w abandoned. That application teaches broadly the applicability, for the above-stated uses, of certain hard nutshells such as Walnut shells and pecan shells, the hard portions of drupes such ascoconut shells, and other hard portions of plant seeds such as the outer covering of the fruit of the Brazil nut tree. These hard materials are ground to a granular form and are employed in wellservicing operations such as drilling. v 7

It has now become possible to define the scope of the invention much more accurately than was possible on the basis of data available when the parent application was filed. The principal purpose of this application is to define more accurately the inherent properties of the materials described in the parent application in terms of i 'recognized tests of the properties of solids so as todis- T tinguish more clearly between operable an'dinoperable .materials.

Thetprincipal object of thisflinvention is to provide an fimproved additive tor wellrservicing liquids suchas drillfiuids and cement slurries, the additive servin to r o; t I t t I V v ries, particularly when the ground plantseeds are us .m

' PlathojP; Scott, Jr., Tulsa, Okla, and'Alfred- 0. Fischer,

al ntsd' 5,,1959.

articlespias in a: ll 'iies reen. are not;

r r" w a i fi e t sm l r s e i q m a seal. 0. a br dge. 911? taining 100,-mesh particles. In addition, this very ii 6 material tends to thicken drilling 'fluids and cement sl high concentrations. Therefore, the ground seeds should 'containnomore than about 10 percent'of particles in'g'alOO-mfesh screen." z V A -M ost drilling fluids contain considerable quantities of particles which willp ajss a number 40 screen and: here}. tained on a number 100 screen, Many drilling flui however, do not contain suflicient material in particle size range to form an efiective seal over a b "d composed of larger plant seed particles. Cement slu usually contain substantially no particles in the '40- to IOO-mesh range. Even those-drilling fluids which contain particles in the 40: to, lOO-mesh range frequently do not form eltective seals over a bridge of larger plant seed particles since the drilling fluid materials are usually tooweak and soft. For these reasons, the additive should contain at least about 10 percent, and preterably about v .10 to 40 mesh; therefore, it may be'desirable to employ particles in this range, the only otherv particles being about an additive containing as much as about 90 percent of percent, should be used, reducing the concentration of torrn permanent. bridges in natural or artificially .c feated :fractures, crevices, fissures,'v u gs; the like. in formar tions penetrated by a well. "Anothenobiect of,the in- 'vention is to provide a well-servicing'liquid suehfas fa "drilling fluid or cement slurry which bridge and seal :natural or artifically created nann es to prevent encessive loss of the liquids from thenvells. Still "another -.object of our invention is to provide a method for servicfing a well whiohjwilltend toprevent f racturing of the :formations and. will seal any fractures which As taught in the parent application,l. it .has now been i found that by useof certainhard portions of plant seeds,

' :ground to certain particle size ranges and shapes and used in certain concentrations, surprisingly fieltective 'bridges and seals can be formed .in and across the crevices, fractures and'the like in formations penetrated by wells; Theterm plant seeds is used broadlytdjnclude -.outer shells such as nut shells, for example lflhe limits on these various factors .willnow be .consideredinmore detail:

PARTICLE'SIZEDISTRIBUTION g p In general, substantially all the additive particlesis'hould jpassa number 4 screen and berfletained on .anurn enlQO :screen. I. These screen sizes, IQgQther with; others ,menrtionedjherein, are US, standard Sieve Series (1 9.4.0)?

3,079. 1 Rarticlesin this sizejrang'e fare normally referred is frequently termed a 30 mesh.scr 'een.

'FinqgSeries Numbers; 2 These are. described, for example, in .Handboolclof ,Chernistryf and Physics, -'p,11;blish dfl py' i, t isachieved. For these reasons, it is generallyadvi ch al u ibe' Pub h ng ed panv, 36th, r i

from'lO- to 40-Inesh material to about or percent. If theadditive contains no particles which Willbe 're-.

If larger particles are present, however, the concentra-v tion of w iQ-EQfb Part cles 22 he redu to as low as about 15 percent. At least thisminimum amount should be present to fill in the large holes between the larger particles and build a base, over which the 40- to IOO-mesh material and fine mud or cement solids can form a. seal. Preferably about 20 to 25 percent of 10- to 40-mesh particles should be present, even when particles coarser than 'lO-mesh are included.

It will be understood that the amount of 10- to 40-mesh particles in the additive can sometimes bereduced below the minimumlimit set above and still iorrn a bridge. For example. s s ant all h S m esul a h gbtai by cutting in-half the amount of 10- to 40-n esh material in the additive and doubling the concentration when the concentration of additive in the slurry "is riot increased. However, the bridge and seal will 'form jmuc h' more slowly so that a large volume of slurry maybe lost to the crevice during formation of such a bridge, In addition, such bridges as do form are sometimeswealeso that several may form and break before a permanentone to observe carefully the minimum limits on ainonn V a J 10- to 40-mmh material set out above. As previously 'rnentioned the additives may conta n substantially no material in the '4'- to IO-meshrange.

In some areas however, crevices, fissures, fractures, and the like are encountered which can be bridged only by such large particles. If material in the 4- to 10-mesh range is included at all, a rather high percentage, preferably about 50 percent, is usuallyremployed. 'As much as 75 percent may be used, the other ingredients being the minimum amounts of 15 percent 10- to 40-mesh, and 10 percent 40- to 100-mesh materials previously discussed. I

Particles which are retained on a No. 4 screen have been found to damage pumps if the pumps can handle them at all. In addition, such large particles tend to bridge across ports in bits, casing cementing shoes, circulating subs, and the like. For these reasons, the additives should include not more than about one percent of such particles, except in extreme cases.

Summarizing the above discussion, the additive should have a particle size distribution within the limits indicated in Table I.

TABLE I Sieve Analysis Percent Present Through Retained 4 N 0t more than 1.

4 0 to 75. 10 40 to 90. 40 100 10 to 80. 100 Not more than 10.

The preferred composition when 4- to 10-mesh material is used is shown in Table II.

TABLE II Sieve Analysis Percent Present Through Retained If 4- to IO-mesh particles are not present, the preferred composition is that described inTable HI.

TABLE III Sieve Analysis Percent Present Through Retained 7 PROPERTIES OF MATERIALS 2,94a,eso

The terms "water resistant and oil resistan will be "employed hereinafter to mean that the material is both insoluble and does not soften seriously when exposed to these fluids for a period'of at least about 30 days. These properties are necessary since the materials will normally be used in the presence of one or both of these liquids. The term oil is intended to mean crude petroleum oilzor a fraction thereof: V

(2) The material should have a softening point of at least about 120 F. if it is to be operable in even shallow wells. Preferably the softening point should be about 300 F. to permituse in deep, high temperature wells.

(3) The specific gravity of the material compared to water should lie' between about 0.8 and 2.0 to avoid excessive tendency of the material to float or sink. Preferably the specific gravity should lie between about 1.0 and 1.5.

4) The material should be strong to resist a tendency to break under the differential pressure which will be built up across the bridge of particles in or across fractures. We have found that the material should have a compressive strength of at least about 5,000 pounds per square inch if it is to be satisfactory for general use as a bridging agent. In this connection, it may be noted that the normal person cannot break in his fingers a particle which will pass a 4-mesh screen if the material has a compressive strength of at least about 1000 pounds per square inch, provided the particle meets the shape specifications set forth hereinafter.

(5) In addition to being strong, that is resisting rup ture under load, the material must also have a high mod ulus of elasticity, that is, it should resist deformation. A material having a low modulus of elasticity will deform so readily that it will flow into fractures rather than bridging them. To avoid an undesirable degree of deformation, the material should have a modulus of elasticity of at least about 10,000 pounds per square inch.

(6) The material must not be too abrasive. It is well known, for example, that sand in drilling fluid exertsa serious abrasive action on steel drill pipe. A convenient measure of the abrasive nature of materials is, the Mohs scale. used by mineralogists. On this scale, common steel has a hardness of about 5; therefore, the bridging satisfactory hard portions of plant seeds incl ude peanut shells, almond shells, cottonseed hulls, and the like. Tests of both operable and inoperable materials have shown that hard seed portions suitable for our purposes should have the following properties:

(1). The material should be insoluble in oil and water I and should not soften seriously in either of these liquids.

material should have a hardness lessthan about 5 to avoid abrasion of steel equipment. On the other hand, the material should not be too soft or brittle or it will itself suifer 'abrasion. and breaking while the slurry is passing through pumps and is flowing in the well. A lower limit of about 2 on the Mohs scale of hardness should be observed to avoid excessive abrasion of the particles of bridging materiaL, This is especially true when the additive is used in drilling fluids which may be circulated down a Well and back to the surface many times during drilling operations. A convenient test to determine if a material is in the required hardness range is to attempt to scratch the material with a common steel nail and with a fingernail. If the material can be scratched by the steel nail and cannot be scratched by the fingernail, it is in the desired range.

We have devised the following simple test for determining the mechanical strength characteristics of the hard 7 plant seed particles. A number of granules of the particular nutshell are prepared which are as nearly as possible of uniform dimensions of 0.1 inch. A Vicat apparatus such as described in the A.S.T.M. Standards 1949, part 3, page 150, is employed. The Vicat needle is employed with the conically pointed needle inserted so that the nonpointed bottom of the needle is just flush with the bottom of the plunger. Positioning the needle in this manner provides a smooth circular flat hard surface which may be used as an impact face. A granule of the nutshell to be investigated is placed Q a steel plate resting on the Vicat apparatus base and the entire apparatus leveled in aobserved for. drilling fluids.

" imme lowered until its base is in contact with the top of the granule and the adjustable indicator is" adjusted on the plunger to be opposite the lowerifzeroapoinf-on the millimeter Scale. The plunger is then -lifted to ahei'ghtiof some arbitrary number of millimeters as indicated by the indicators opposite the scale and the plunger abruptly reg This number is termed the strength factor. All the tests" that we have performedindicate that it is highly desirable to employ a material which gives a strength factor reading of about 20 or greater.

In" cement slurries, the same general concentration ranges apply as in drilling fluids. In practice, however, it ,iscustomary to employ high concentrations of at least .fabout 20 .to 30 pounds of walnut shells per barrelof cement slurry; As much as about 60 pounds per barrel are sometimes used. The increased cost of higher con It will be understood that mixturesof materials meeting a the above requirements may be used. For example, when reference is made hereinafter to a single material such as 'the hard portion of a plant seed, the term is intendedf' '20 to indicate either seeds of a single species of plant or mixtures of seeds from several types of plants.

PARTICLE SHAPE Two factors of particle shape are important: first, the particle should be granular as distinguished from fibrous or lamellated, that is,"from a central point it should have approximately'the same dimensions in all directions. ,If the particles are long or fiat, they tend to be much weaker than granular particles with thesame maximum dimension; therefore, fibrous or'lamellated bridging agents falling within a given size range 'as determined by sieve analysis form .a much weaker and less effective bridge than granular materials in the same range of sizes. A convenient measure of the granular nature of a particle is. illustrated in Stratigraphy and Sedimentation by W. C. IKrumbein and L. L. Sloss, 1951 edition, published by W. -H. Freeman and Company. f Page 81 of this refer- 'ence presentsa comparison chart by which the average sphericity factor of particles can be determined. The same chart also permits determination by comparison of the centrations is small and the importance of sealing frac; tures is very great. .A concentration suificientto provide a large safety factor over the minimum concentration thought to be eifective is generally considered advisable under these circumstances. a V

'METHODS oF APPLICATION The slurry of bridging additive in the supporting liquid can be prepared in a number of ways. In-one method, the. additive may be premixed with other dry materials such as clay or weighting agents for drilling fluid, or dry cement for cementing slurries. The dry mixture, can then be added to the liquid as it is pumped into the well. Prefsecond important factor.. This is the angularity of the 1 particles. It aparticle has manysharp angles and points,

itinterlocks with other similar particles more readily to form an eifecti've'bridgethan if the edges and corners are CONCENTRATIONS .7 The recommended concentration of bridgingagentin operation inwhich the slurry-is to beused and in part on the particular type of material employed. "Normally at least about 2 pounds of the preferred material, Walnut shells, should be used per barrel of drilling fluid. For the softer, weaker, and less ,angular materials. falling within 'thellimits outlined above, -2 pounds perg barrel should be regarded as an absolute minimum limit. An upper concentration limit of about; 25 or 30 pounds per barrel is usually This is principally for economic, reasons. From a technical v standpoint, use of even higher concentrations, for example up to about 60 pounds per barrel, is not objectionable. and usually pro- .duces at least slightly stronger bridges in a slightly shorter :time than when concentrations below about 30 pounds .per barrel .are employed. The ultimate upper concentra- .ttion limitis slightlybelow the concentration atwh ch mufiicicnt' finely divided additive is present to thicken the I drilling fluid to such a degree that it becomes unpiimpable.

the slurry depends in'partlon thepaiticular type of well erably proportioning means should be employed to insure circulated down the well through a pipe and then up the well around the outside of the pipe. In casing cementing operations, the slurry may or may not be circulated to the surface outside the pipe. In drilling operations, on the other hand, the slurry is generally circulated to the surface and back down the pipe after suitable treatment. In

casing cementing, the bridging additiveis generally maintained at a suitable concentration in the slurry at all times. It is possible, however, to include slugs of the granular additive in small batches of the cement. This batch treatment is widely used during drilling operations, that is, a

small batch of drilling fluid containing walnut shells, for

example, is mixed and is pumped into the well as a separatep'lug in the drilling fluid. As this plugof slurry coritaining a high concentration of bridging agent passesthe zone to which drilling fluid is being lost, ittends to enter the fractures or crevices and bridge them. The following drilling fluid then completes a seal over this bridge'to prevent further loss. 1:.

' In squeeze cementing operations, the entire slurry may contain thegranular bridging additive. Sometimes, however, it is preferred to pump a considerable amount of neat slurry into the zone to be squeezed in order to fill the fractures and crevices before the bridging agent is added. The granular additive then bridges the crevices and a seal is formed over these bridges to permit developmen-t of the desired squeeze pressure. So-called lowwater-loss cement can be used with considerable advantage in combination with granular bridging agents in squeezing operations to avoid excessive dehydration of cement slurries which might lead to improper setting. Y

Our invention will be better understoodbylconsidering the following examples: Example I To determine the suitability of various hard: portions i of plant seeds, their properties were tested. results are presented in Table IV.

Water resistance of materialswas determined by soaking them in water for about a 'monthl' Several ofthe plant seed materials such as peanuthulls, cottonseed hulls,

orange seeds and watermelon 'seeds' were eliminated on this basis alone. Most of the harder seed materials, however, were found to be quite satisfactory from this'sta'ndpoint.

Specific gravity was determined, most cases, by

In drilling and casing cementing practices, the slurry is I TABLE IV V f Y I I Compres- Modulus Hardness, Average Material Water Specific sive Elsa, Mohs Thickness,

' Resistant Gravity Strength, p.s.i.. Scale 1 in.-

' p.s.i.

Black Walnut Shells 1.3-1. 4 20, 000+ 170, 000. 0.20 Pecan S 1. 3-1. 4 5, 000+ 10, 000+ 2-4 0. Coconut Sl1ells 1. 4 5, 000+ 10, 000+ 3 0.10 Peach Pits Yes 1.3-1.4 20,000+ 10,000+ 3 0.15-0.25 Brazil Nut Covers 7 I Cherry Pi ts 1. 3-1. 4 5, 000+ 10, 000+ 2-4 0. 05 Apricot Pits 1.3-1. 4 000+ 10, 000+ 2-4 0. 08 Hickory Nut Shells- 1.3-1.4 20, 000+ 220, 000 3 0. English Walnut Shells. 1. 3-1. 4 5, 000+ 10, 000+ 2-4 0.04 Plum Pits 1.3-1.4 5,000+ 10,000+ 2-4 0. 06 Olive Seeds.-- 1. 3-l. 4 5, 000+ 10, 000 3 0. 06 Prune See 5... 1. 31.4 5,000+ 10,00 24 0.04 Grape Seeds...- 2-4 0.02 Almond Shells. 1. 3-1. 4 5, 000+ 10, 000+ 2-4 0. 03 Peanut Hulls V 2 0.03 Cottonseed Hulls 2. 4 0. 02 Acorn Shells Yes 1 31 4 5,000+ 10,000+ 2-4 0.02 Orange Seeds Nn 2 0; 02 Grapefruit Seeds No 2 0. 02 Lemon Seeds N0 2 0. 02 Waltermelon eeds 7 No 2 0. 02

dropping samples of the materials into liquids of various densities and observing whether they sank or floated. I

In the case of the coconut shells, however, the density 7 was determined by use of a pycnometer. The specific gravities of all the hard seed materials tested were remarkably similar and fell well within the desired limits. Compressive strength and modulus of elasticity were difiicult to determine due to the small sizes of the particles available for-testing. Large enough pieces of the walnut shells and hickory nut shells were obtained for measuring these properties with a fair degree of accuracy. It

.was possible to determine that other materials, such as pecan shells and peach seeds, greatly exceeded the minimum requirements, although accurate values could not be measured in most cases. No effort was made even to estimate strengths of materials which were not sufliciently thick to form particles having the proper shapes, or which were not water resistant or hard enough. Hardness was determined .by means of a scratch test .using materials of known hardness. In some cases, particles of a single type of seed material seemed to vary .in hardness. In some cases, available samples had rather uniform hardness. No seed material was found which was toohard. Many were found which were too soft.

. A very important factor is the shell thickness. At least some large particles should be present in the ground product. Even if the composition is to be that described in Table III, for example, some of the particles must be retained on a 16-mesh screen and some should, preferably, barely pass a IO-mesh screen. The sieveopenings for 10- and 16-mesh screens are 0.079 inch and 0.047, inch, respectively. Thus, the maximum dimensions of some of the'particles should be at least about 0.05 inch, and

preferably, for some at least, about 0.07 inch. In order to have a Krumbein sphericity falling within the specified limits, the minimum dimension of the particles should not be less than about one-half of the maximum dimension, and preferably should not be less than about threefourths the maximum. Thus, the-thickness of the original shell should theoretically be at least about 0.025 inch and preferably at least about 0.04 inch. This checks closely with the results reported in Example IV which show that almond shells, having an average thickness of only about 0.03 inch do not form 10- to 16-mesh particles 1 having an average Krumbein sphericity of at least about 0.4 and do not form a suitable alternate to materials such as ground black walnut shells and ground coconut .shells. English walnut shells, on the other hand, with an average thickness of about 0.04 inch, have been found to produce a satisfactory-ground material.

The shells typically vary in thickness from point to point in a single shell. The values given in Table IV are average figures for the entire shell. The only exception W is peach pits. Peach seeds are completely covered by closely spaced ridges. Therefore, a range is given showing the average thickness from the inside of the shell to the peaks of the ridges and the average thickness tothe bottoms of the valleys between the ridges. It will be noted that the thickness even at the thinnest point is greater than the thickness of most other shells.

Example II Tests were run to determine the crevice-sealing ability of ground black walnut shells. In these tests, various concentrations of the shells were added to drilling fluids. The drilling fluids were then pumped through slits of various widths and the concentrations necessary to seal the slits were noted. The drilling fluids had a viscosity of 50 to 1 00 centipoisesas determined by a Stormer vis cosimeter-rotating at about 600 rpm. and a fluid loss of about 15 to 20- cc. as determined by the standard test described in API Code No. 29, second edition, July 1942 (tentative). The particle size distribution was that given in Table II. The average Krumbein roundness of the particles was about 0.3 and the average Krumbein sphericity was about 0.7. r The results of these tests are presented in Table V.

' TABLE v Slit Width, Concentration, lbsJbbl. inches 6'20. maximum.

The pump employed in these particular tests developed a maximum pressure a little less than 1000 p.s.i. Therefore, if the maximum pressure developed, the seal would withstand at least 800-1000 p.s.i. This is believed to be considerably in excess of most pressures developed in drilling operations or in casing cementing. In squeeze cementing, the pressure sometimes exceeds this range, of course, so development of a seal which will withstand at least this pressure is considered to be veryimportant.

It willibe noted that use of only one pound of nutshells per barrel of drilling fluid permitted sealing fairly large slits in the range of 0.14 to 0.16 inch in width. For wider slits, higher concentrations had to be used. In other tests, WithveryanguIar materials, as little as 2100015 li'k I pounds of per jdrill Jnglluid; was able to form aseal'over a slit 0.20' iuch in l Sieve Analysis i Concem v n r Slit; Sealing .tration, I I I 1 Size, Pressure, 1054001. 04 4-10 1040 40-100 Thi'glgh inches -p.s.i.'

"0.4 08.8 22.9 -7.7 I 0.-2 0.06 maximum. 0.4 68.8 22.0 7.7 0.2 0.08 460. 0.3 54.3 18.1 27.1 0.2 0.08 maximum. 0.3 54. 3 1s.'1 27.1. r 0.2. 90.10 000. 0.2 4418 15.0 39.9 0.1 0.10 maximum 02 44. 8 15. 0 39. 9 0.1 0. 12 Do. 0.2 44.8 15.0 I 39.9. V, 0.1 0.14 Do. 0.2. 44.3 15.0 39.0 1 0.1 0.10 Do. 0.2 44.8- 15.0 39.9 0.1 020- 300.

0.-2 514.8 15.0 39.9v I 0.1 0. 20 maximum 0.2 44.8 15.0 39.9.. 0.1 0.22 Do.

'- It is apparent from these results that ground coconut shells, when used with theproper particle size distributionIare as-good as ground black walnut shells. Two

.pointsshouldbe noted. First, probably due to the flatten shape .of theparticles, lowerconcentrations of the ground coconut shells did not seal quite as well as the more granular ground walnut shell particles. Second,

the-te ts show that as little as 15 percent particles in-the -10 40-rnesh range'are enough to fi1li .;the'holes.be-.; ilargenparticles sed to bridge vwide slits, crevices;

Example. IV

'ticles was about 0.2., .The average Krumbein 'sphericity F-Fabl manna vrr I Slit {Sealing Free? I Liquid Width,

boneentratlomlbsflbbl.

the outer layerfi's' soft and, fibrous. O'iil'y'the inner'layer,

width,"which would withstand about 900 p.s.i. pressure. 7

The proc'edureoutlihed ini Exanrple n was/employed ,to test ground almond. shells as a bridging agent. I The V .particlesize distribution wasvery close 'to that set outi rame II. The average Krumbein roundnessofjthelparwas about '0. 2. Results of the. tests are reported in I me h d 'd'eis'c' i' i' d. nfimm le d to evaluate the crevice-sealing abilities of several cornmercially available lost circulationipreventive additives.

r A mixture of sawdust and textile fibers was added .to

- 'iii sb t I 1 'lfo obtain" a clear-cut evaluation of the importance of fangularityj the procedureoutlinedin Example II was employed jt'o c rnp'are the'bridging abilitieslfdf angular and? rounded particles. of black walnut shells. Angular particles were obtained by grinding thefshells in an attritionfr'n'ilL Rounded particles were obtained by grindingthe shells in a hammer mill, the sample being rerun through the mill four times to round oil? the sharp corners and edges. The samples of both angular and rounded particles were carefully screened into various 'size ranges and reblended to be sure the particle size distributions. were the ,same. 'Both blends contained the particle size distribution indicated in Table VIII.

' v TABLE VIII Y Particle Size, Sievc No.

Percent r 7 Through Retained The angular particles had a Krumbeinsphericity of about 0.7, and a Krumheinroundness of about 0.2. For the rounded particles, the comparable figures were 0.8 and 0.8, respectively."

Results of fracture sealing tests are shown in Table IX.

I TABLE IX Ooucen- Slit Size, Pressure, "IypeMatenal; .tration, inches p.s.i.

' 1bs./bb l. I I

s he ical-.. .20 0.20 a 0 Angular--. 20 0.20 2, 300' I The importance of angularity is 'very apparent from these results. j 1

' E mple V1.

drilling fluid in a concentration of 10 pounds per barrel. This bridging agent would not seal a slit more than mud so that after three days exposure, the sealing-capab'ilities wel'e "serious ir'npaired Expanded perlite, screened-to the particle distribution described in Table II, ='when {added to 0 d'rilling'fluid in a concentration of -'"'"60 to 80 poiiudsper barrel would not 'se al 'a fracture lmor'e than 031 inch wide.

Wood ch'ps grolind 't pass a -4-rnesh screen and be retained on a l00-mesh screen with particles distributed throughout the range were added to a drilling fluid in a concentration of 10 pounds per barrel. Initially .a slit was sealed having a Width of .12 inch. The seal withstood a differential pressure'of 900 p.s.i. before break- 651.

mg. When the seal was re-estab-lished and allowed to *Ystan d for three days, however, the wood chips had sofwhieh hasan average thickness of about 0.03' inch, is

sufiicientlyxhard :and strong to rneetaourj requirements. These t hin shells 'can'not df .cours eabe ground 'to form coarse particles of a suificiently;granular"shape to beat;

larger t an a out 30 e on t ve-e1 .avel li m-Y bein sphericity greater than about 0.4.-

' p.s.i. IUW V V I j fVesiulated-polyst-yrene was 'groundto. passa 4-mesh 0 "cles distrihutedthrou-ghout the range.

tened to such adegree. that the seal withstood only 400 screen andbefi'etai'nied on a IOU-mesh, screen with parti- A concentration of 20 poundsfper' barrel; of this material in drilling fluid I would hot seal-a fracture over .075 inchwide since the polystyrene crushed, due to the presence of air bubbles in the polystyrene, and'flowed through larger slits.

Example} In the Procter A-Z well, .Spraberry Field, Glasscock County, Texas, mud returns were lost 'at 5,315 feet. Large quantities of plant fibers and cottonseed hulls barrels ofv thisv batch weredisplaced .into the pipe were added to the drilling fluid in an attempt to regain 5 no further loss of mud b t a week shale circulation The same Zone kept breaking down shaker was bypassed during th1s time to avoid removal ever, on two subsequent days. The first time comof the nutshells At the end of a week h mud a plete circulation was lost and 65 barrels of mud were h hl shaledshlakelr again Two days a pumped into the formation before the loss could be 058 9 anon Starte sow Mmeygmund w m stopped. The second and third times, 175 and 225 10 shells were then added in a concentration of about 8 rels were lost, respectively. When ground walnut shells gg g g i gg was lmmeqlately i arrived on location, the rate of mud loss was up again establs g er d cu ty occurred m dnnmg to about 125 barrels of mud per hour and only about 25 to a out 0 percent of the mud being put into the well was being Example X recovered. The cost of the plant fibers, cottonseed hulls, and other lost circulation materials that had been tried T A i 5 83 East Fleld fii -ii was more than $1 600. Estimated loss of rig time brought 08 percent 0 t e retun-1S W e n a the total cost up 1 $1 900 bridge in the well at 4,802 feet. In six and a half days, 3000 barrels of mud containing about 40,000 pounds of g g ig g giii aig i ga gggg fii z gg plant fibers, cottonseed bulls and chopped cellophane were in Table II were added to about 100 barrels of mud lost' A batch of mud was then- Prepared cont-Emung to roduce A concentration of about 10 ounds er bar- 50 sacks ground walnut Shells m concent'ra-tmn pf This batch of was pumped pdown g drill about 42 pounds per barrel of drilling fluid. batch pipe and was followed by ordinary drilling fluid; Withgigs? g g igg j i z ggggggfl g :5 fil i in 15 minutes, circulation was restored. Nonadditional taming thegr'oun'd Shells down'to the thief zone operw 12: fi i 3 1;581: 5 Zjfijgfiflfifi: g2: 'tions stopped while a new pit of mud Was mixed. Circut 1 $215 y lation was then re-established and only 35 more'barrels appr lma y of mud were lost in cleaning out the bottom of the well Example VIII and reaming a core hole which had been drilled. The A well in the Pegasus Field Midland County Texas trouble witht lost circulation was entirely overcome. Mud was being drilled using drilling fluid containing both plant ilsed thls case was a 15 percen} crude 011 emulsloll fibers and chopped cellophane. Complete circulation m the aqueous. phase contamed Starch and b was lost at 6,683 feet. A batch of drilling fluid containtonne The mud weight was pounds per f f ing fifty sacks of ground walnut shells as described above Example Xl v 1 was mixed in the suction pit to establish a nutshell con- Casing was cemented in 9 deep wells in a Ycemrafion of abfmt 30 l barrel. By the time Area of West Texas In some wells the cement includ- .0 5 w iein some no nuts e s were use epartice size of the highly fractured shale section. The mud system at this fi g ggi I The Hawks of tests are epo'rte are: ras?assessment 325: .5 fill w r obtained Another batch of mud containin 30 ounds Survey 10mm the top of the cement Ebeh-u-1d the casing Per barrel of nutshells was prepared as before When the golume of hole the casing y t e vo ume o cements urry use e most'imthls fi ig sg i g i igh 23521: portant point to be noted is that in spite of a higher gig am e density slurry being used when nutshells were added, a 1 E l IX T the percent fill behind the casing was much higher than m l 1 when the nutshells were not used. The apparent fill of In awell at Bastian Bay, Plaquemine Parish, Louisiana, more than percent comes about due to bypassing lost circulation, occurred'while drilling at';112,096 feet of some drilling fluid by cement. This is a common .using a 17 pounds per gallon drilling mud. Various occurrence in casing cementingoperations and undoubtlamellated materials, including mica flakes .as well as g f edly occurred when the nutshells were not used. 'Infact, some fibrous materials, were added, in accordance with by passing was probably worse when nutshells were not normal field procedures in this area. Circulation was present. The reason is that the degree of bypassing denot regained. A 500 barrel batch of mud containing pends upon the rate of flow of the slurry. Greater by- 2500 pounds of ground walnut shells was prepared, 100 passing occurs at lower rates of flow. When nutshells TABLE X Lost circulation ma- (lost, dollars Expanded terial,lbs./Sack cement Slurry Well Cement Perlite Wtz, lbs./ Percent sacks emit. gal. Fill v Cellophane Nutshells Per emit. Perit.Lin-

Flakes Slurry eal lilll s00 0 0 12.7 75 .1. 32 0. 74 950 54 0 12.7 91 4 1.55 0. 54 950 M 0 13.2 94 1. 5s 0. 54 1,150 $4 0 13.2 91 1 1.53 .o.71 s00 54 0 13. 2 as 1. 53 o. 64 0 o 2 14. 7 1. 64 o. 44 0 0 2 14.7 117 1.64 .0.55 0 o 2 14.7 115 1.64 0.55 0 o 2 13.7 1. as 0-. a2

. er tatesgof fiow and c n ass nt i sing or mud. Another A point. to

the new waits: to ate.- 1

a b id i s} r r' iiinthe demen ia 'tion inflt ec s ngyf,

, be'mot alth'u'gh he of nt-slurryper I Q veiaeeqmplish'ed the object'sfof our 9902M; wea sen ,eteater wh nnutshells were 5 r d; additijvefdr Well-servicin'gjliguijds \{sed than n y e QYQ Z gfilf-QQSPPE' 8 611,215]. g iiidsjand 'ce'mentslurries has been-pro- $99! f h l :ihiq l fq l VYi t ha b n show h t h sa di ive anjhee decreased. U 4 ployed to form adrilling fluid or a cement slurry, hich 4 r. Exampleqxlll, will bi dge 'and slea atjural or artificiallycreated ftaea r t 10 t ures to preventj exee'ssive losso'f these liquids from the 3;,fieventeenrsqueezq; cementing. jobs were performed in wells.- Methods have been provided for use of the addisix wells intlre, Andrews Area, of West Texas. In, some Vtive and slurries prepared from it. t I hbs gmnnd putshells were used and in sometheywere ,lillekglaiin:v g V g t 11 Gags, m h u h g 1 rti l ize diss- 1. A drilling fluid including a lost circulation'recovery fuihgtipn sgt gut in imp 1; 1 11 'Ijh results oi the tests 15 material comprising granulated strong plant seedparticles r nst tuted in Table XL: -The ecision as to whether a i g a strength factor of about 20,. a subthenob-was successful or notand the remarks are taken stantial amount of. the particles being retained on a 3.0 {rou ine field report of the tests. meshjsleve', and'msufiieient of the particles passinga 1100 TABI E XI t i SqueezePress.,p.s.l. Depthflt. Material used Success Remarks, V Maximum Final i] "aosreaqso zoosacks neat eement 4,200 new Cement was displaced behind easing with 10 .r r t barrels water.at-1,800 p.s;i. v 2 9, 0379,080 --.do. 7,200 7,200 No Drill stem test recovered drilling mud and 1 7 salt water after drilling plug; 3 -9,037-9,080 --d0 5,4001: 2,200 'No...-.- Before. and ofjob, ressure declined to 2,200 t p.s.l. Cleared tool and perforations. 4, 0037-0080 fiilsacksneatcement,followedby150 0,500 0,500 Yes Tested perforations at 2,500 p.s.i. for I saclr s with 4 lbs. nutshells per v minutes. V

.sae H. it t 5 1. 8,750 100 sacks neat cement 0 0* No. Cleared tool and perforations.

""' 2 8,750 100 sacks neat'cement, followed by 4,100 2,800, Yes, 'Tested at 2,000 p.s.l. for 30 minutes. :1 I 1 sacks with 4% bentonite and 4 s, i i

l r V lbs. nutshells per sack.

13,953-14,000 150sacks neat cement .0 1 0' No.. Cleared tooland openhole. 2; 13,05,3,-14,000 100 sacks neat cement, followed by .5, 800 4 5,800. Yes None. 7

1 100 sacks with 4% bentonlte and 1 41bs.nutshe11spersaek. t v 13, 053-13, 96 5. 150 sacks neat cement, followed by 5, 800 '5, 800 Yes Swabbed 100 ercent water. f 100 sacks with 4% beutonite an l d lbsl nutshells persack. t 4 '13,930-13,944' 1 5,900 :5,900 Yes-...- -None. V V

p 13, 125-13,.773 100 sacks neat cement,-=iollowed by 6,000; 6,000- Yes..- Perforatlons swabbed' 30 barrels water per 7 100st: kswith, 4% bentonite and t g y 4 hour. hellspersack t V V i r 1 0 No Periorations thought to be open to cavity V encountered'at 13,276. x w

v a'e a- ,p.s.-. on es. erora'ons' 10%iiikiiviiii $iisfi iiiti sfii 4,000 4,000 egg t ggg ggggggg g gg wgg 3 33-333 r 1 nutsheus per 9 an1d 4,000ga1s. acidtrac withl Ib. sand-per i T #38. W 100.s,ack s neat cement 1,200 0 vNo Squeeze required to repairholeincaslng, V 100 sacks neat cement, followed by 1, 750 1, 250* No.-.-.. Cleared retainer and holeinplpe. 50 sgckswithd lbs.-nutshells per I i 7 i v, S50 50 sacks neat cement, followed by 100 4,650. 4,550 Yes Reversed'out sacks with 4 lbs. nutshells sacks with 4 lbs. nutshells per q v- 7 per sack. Casing tested at 2150 psi. or

seek; V 30'minutes. do 3,000 0,30%.-." None 1 ..'Ihe;?most, i P l SS ive fact to be noted from Table XI is thatiiniseveralof the we1ls, neat cementsqueezes were .attemptedwitheut suceessn- In well'No. 1, for example, xrthreeis'queezes with neat-cement were employed in unsueee'ssfiul attempts to squeeze off a zone. 7 idfid-pounds ofynut s hells per sack of cement made possible The addition successfully squeezing off all of these zones. 'It' will be finetedthat inzsome cases e en h P e of nutshells urna''insllfl eient toprevent loss of the cement slurry to the-formation, jexamplqin job No.6 on well No. 3, *IheJrPeIEfQEatidHQ apparently wereopen to a cavern. In ather aeases,='thej failure of the squeeze cementing job,

y evenwhemnutshells we e u e m y h n ue to q ti-loss'flta Qavesnswgr to ,crevices 'too large tov be sealed by ;the ne'rtieles e-nutshells employed. .111 atleast some of :ithelewcalses', =the-use ofthe'particle size distribution described in Table II rather than the smaller particles set .-eutim'1? b1e1-nrwen1 probably have resulted insuccess e e iebs ,;;Use et e-tiner did z distribution in squeeze cementingis generally more desirable to mesh" sieve to cause said drilling fluid to become too viscous to be 'purnpable, said strong plant seed particles being in a concentration of at least about 2 pounds per barrel, of saidfiuid. V

12'. A drillingfluid containing granulated strongplant seed particles having a minimum strength'factor of about 20,, substantially all of which pass through a 4 mesh sieve and are retained on a 10 mesh sieve, said plant Seed particles being'in a concentration of at least about 2 pounds per barrel'of said fluid.

3. A drillingflnidincluding a lost circulation recovery material comprising granulatedstrong nutshells having a f li'nimnni lstrength factor of about 20, a substantial amonntfof said material being retained on a 30'mesh sieve, and insuflicient of saidmaterial passing a 100 mesh sieve to increase excessively the viscosity of said drilling ui'd' 'js aidstrong nufshells being in a concentration of at about 2Qpounds per. barrel of said fluid. V A drilling'fluid containing granulated nutshells having a strengthfactor of about 20; substantially in u m e s descri tion and all of which pass through a4 mesh sieve and are retained on'alO mesh sieve, said nutshells being ina' concentration of at least about 2 pounds per'bar rel oflsaidlfluid;

5 A drilling fluid containing granulated nutshells hav-' ing a minimum strength factor of about .20, there being at least about 1 pound of said nutshells-per barrel of said fluid'in a size gradation from granules passingthrough a 4 mesh sieve down 'to those retained ona 10 mesh sieve, and there being at least aboutjl'poun'd of said nutshells per barrel of'said fluid substantially allof which pass through a 10 mesh sieve and are retained on a 100 mesh sieve.

6. A drilling fluid containing granulated nutshells havmg a minimum strength factor of about 20, there being at least about 1 pound of said nutshells per barrel of said fluid in a size. gradation from granules passing through a 10 mesh sieve down to those retained on a 16 mesh sieve, and there being at least about 1 pound of said nutshells per barrel of said fluid substantially all of. which pass through a 16 meshsieve and are retained on a 100 mesh sieve. 7. A drilling fluid containing granulated nutshells hav: ing a minimum strength factor of about 20 in a concentration of from about 2 to about 60 pounds of said nut-. shells per barrel of said drilling fluid, substantially all of which pass through a 4 mesh sieve, about half of the nutshell granules passing through a 10 mesh sieve and substantially all of said granules being retained on a 100 mesh sieve.

8. A well-servicing composition comprising a slurry, and from about 2 to 60 pounds of an additive per barrel of said slurry, said slurry being of the class consisting of aqueous drilling fluids, non-aqueous drilling fluids and Portland cement slurries, and said additive consisting essentially of granular particles of a water-resistant, oilresistant, hard portion of a plant seed having a compressive strength of at least about 5,000 pounds per square inch, a modulus of elasticity of at least about 10,000 pounds per square inch, a hardness between 2 and 5 on the Mohs scale, and a specific gravity between about 0.8 and 2.0 compared to water, said particles having an average Krumbein sphericityof at least about 0.4 and said additive consisting of not more than 1 percent ofsaid particles retainable on a number 4 screen, from about to 75 percent particles passing a number 4 screen and retainable on a number 10 screen, from about 15 to 90 percent particles passing a number 10 screen and retainable on a number 40 screen and containing a substantial amount of particles retainable on a number 30 screen, from about 10 to 80 percent particles passing a number 40 screen and retainable on a number 100 screen, and not more than about 10 percent particles passing a number 100 screen, all percentages being by weight.

9. A well-servicing composition comprising a slurry, and from about 2 to 60 pounds of an additive per barrel vof said slurry, said slurry being of the class consisting of aqueous drilling fluids, non-aqueous drilling fluids and Portland cement slurries, and said additive consisting essentially of granular particles of the water-resistant, oilresistant, hard portion of a plant seed having a compressive strength of at least about 5,000 pounds per square inch, a modulus of elasticity of at least about 10,000 pounds per square inch, a hardness between about 2 and on the Mohs scale, and a specific gravity between about 0.8 and 2.0 compared to water, said particles hav ing an average Krumbein sphericity of, at leastabout 0.4 and an average Krumbein roundness of not more than about 0.6, and said additive consisting of not more than 1 percent particles retainable on a number 4 screen, from about 0 to 75 percent particles passing 'a number 4 screen and retainable on a number screen, from about to 90 percent particles passing a number 10 screen and retainable on a number 40 screen and containing a substantial amount of particles retainable on a number screen, from about 10 to 80 percent particles passing a number 40 screen and retainable ona number 100 screemand not more than about 10 percent particles passing a number 100 screen, all percentages being by weight.

10. The composition of claim 9 .in which.

portionof a plant seed is black walnut shells.

, 11. The composition of claim 9 in whichsaidslurry isla, drilling fluid. 7. t.

12. The composition of claim '9 in'which saidslunfy is a suspension of Portland cement in water. 13. The composition of-claim' 11 in which said hard portion of a plant seed is black walnut shells. -14. The composition of claim '12 in which said" hard portion of a plant seed is black walnut shells. 15.. vA liquid composition for sealing a coarse grained porous formation traversed by a well bore comprising a drilling fluid and particles ranging in particle size"from 4 mesh to 100 mesh, such particles being of hard portions of plant seeds selected from the group consisting of black walnut shells, pecan shells, coconut shells,peach pits, cherry pits, apricot pits, hickory nut shells, English walnut shells, plum pits, olive seeds, and prune seeds.

16. A drilling fluid including alost circulation recovery material comprising granulated strong plant seed particles selected from the group consisting of black walnut shells, pecan shells, coconut shells, peach pits, cherry pits, apricot pits, hickory nut shells, English walnut shells, plum pits, olive seeds, and prune seeds a substantial amount of the particles being retained on a 30 mesh sieve, and insuflicient of the particles passing a 100 mesh sieve to cause said drilling fluid to become too viscous to 'be pumpable, said particles being present in a concentration of at least about 2 pounds per barrel of said fluid.

17. A drilling fluid containing granulated strong plant seed particles selected from the group consisting of black walnut shells, pecan shells, coconut shells, peach pits, cherry pits, apricot pits, hickory nut shells, English walnut shells, plum pits, olive seeds, and prune seeds, substantially all of which pass through a 4 mesh sieve and are retained on a 10 mesh sieve, said strong plant seed particles being in a concentration of at least about 2 pounds per barrel of said fluid.

18. A process fordrilling a well comprising circulating in a well a drilling fluid containing a lost circulation ret a substantial amount of the particles being retained on a 30 mesh sieve, and insuflicient of the particles passing a mesh sieve to cause said drilling fluid to become too viscous 'to be pumpable, and contacting the walls of said well with said drilling fluid to form a bridge and seal over the formation openings through which drilling fluid is normally lost.

19. A process for drilling a well comprising circulating in a well a drilling fluid containing a lost circulation recovery material comprising granulated nutshells having a minimum strength factor of about 20, a substantial amount of said material being retained 'on a 30. 'rnesh sieve, and insuflicient of said material passing a 100 mesh sieve to increase excessively the viscosity of said-drilling fluid, and contacting the Walls of said well-with-said drilling fluid to form a bridge and seal over the formatio'n openings through which drilling'fluid is normally lost.

20. A process for drilling a well comprising circulating in a well a drilling fluid containing a lostcirculation recovery material comprising a gradation of sizes of granulated nutshells having a minimum strength factor of about 20 with a sieve analysis of through 4 mesh and over 100 mesh in a concentration of at least 2 pounds per barrel of said drilling fluid, and contacting the walls of said well with said drilling fluid to form a bridge and seal over the formation openings'th'rough which drilling fluid is normally lost. I v

21. A processfor drilling a well comprisingcirculating in a ovell a drilling fluid containing a lost circulation recovery material {comprising {a gradation of sizes ,of

granulated nutshells having a minimum I strength factor of about 20 with a sieve analysis of all through 4o mcsh," at least about halfbeing retained on a 10 meshscreen'; and substantially 'all bein'g'retained on a 100 mesh screen in a concentration of from 2 to .60 pounds per barrel ofdrilling fluid, and contacting the walls of said well with said drilling fluidtoform abridge'and seal over fgcgaaso 0.6, "andsaid additive consisting of not more than 1 percent particles retainable-on-a number'4 screen, from; j

about to 75 percent particles passing a' number 4 screen and retainable on a number 10 screemfrom about r 15 to 90 percent particles passing a number 10 screen and retainable on a number 40 screen and containing a the formation openings through which drilling fluid is l i normally lost.

- resistant, hard portion of a plant seed having a compressive strength of at least about 5,000 pounds per square inch, a modulus of elasticity of at least about 10,000

pounds per square inch, a hardness between about 2 and 5 on the Mohs scale, and a specific gravity between about 0.8 and 2.0 compared to water, said particles having an average Krumbein sphericity of at least about 0.4, and said additive consisting of not more than 1 percent particles retainable on a number 4 screen, from about 0 to 75 percent particles passing a number 4 screen and retainable on a number screen, from about to 90 percent particles passing a number 10 screen and retainable on a number 40 screen and containing a substantial amount of particles retainable on a number 30 screen, from about 10 to 80 percent particles passing a number 40 screen and retainable on a number 100 screen,

and not more than about 10 percent particles passing a number 100 screen, all percentages being by weight.

23. A method of servicing a well comprising circulating in said well a composition comprising a slurry, and from about 2 to 60 pounds of an additive per barrel of said slurry,'said slurry being of the .class consisting of" aqueous drilling fluids, non-aqueous drillingfluids and 40 Portland cementslurries, and said additive consisting es-a v sentially of granular particles of water-resistang oil-resistant, hard portion of i a plant seed having a compressive strength'of at least about 5,000 pounds per square inch,"

fsubstantial amount of particles retainable on a number 30 screen, from. about 10 to percent particles passing a number 40 screen and retainable on a number screen, and not more than about 10 percent particles passing a number 100 screen, all percentages being by weight.

24. The method of claim 23 in which said hard portion of a plant seed is black walnut shells.

25. The method of claim 23 in which said slurry is a drilling fluid.

26. The method of claim 23 in which said slurry is a suspension of Portland cement in water.

27. The method of claim 25 in which said hard portion of a plant seed is black walnut shells.

28. The method of claim 26 in which said hard portion of a plant seed is black walnut shells.

29. A process for drilling a well comprising circulating in said well a drilling fluid containing a lost circulation recovery material, comprising granulated strong, plant seed particles selected from the group consisting of black walnut shells, pecan shells, coconut shells, pe h pits, cherry pits, apricot pits, hickory nut shells, Eng ish walnut'shells, plum pits, olive seeds, and prune seeds, at

substantial amount of the particles being retained on a 30 mesh sieve, and insufficient of the particles passing a 100 mesh sieve to cause said drilling fluid to become too viscous to be pumpable, and contacting the walls of said well with said drilling. fluid to form a bridge and seal over the formation openings through which drilling fluid is normally lost.

References Cited in the file of this patent UNITED STATES PATENTS 2,319,182

OTHER REFERENCES Rogers: Composition and Properties of Oil Well Drilling Fluids, 1st ed., pub. 1948 by Gulf Pub. Co. of Houston, Texas, pages 449 and 450. 

